In recent years, in internal combustion engines of vehicles or the like, an improvement in performance, such as fuel consumption and air exhaustion, has been achieved by varying the valve characteristics of an engine valve (intake and exhaust valves) according to engine operation status. A valve working angle variable mechanism for varying the valve working angle of an engine valve has been put into practical use as a system for varying a valve characteristic.
FIG. 12 illustrates an example of the above mentioned valve working angle variable system. The valve working angle variable system illustrated in FIG. 12 includes a valve working angle variable mechanism 1, and an actuator 2 that drives the valve working angle variable mechanism 1. The actuator 2 includes a motor 200, a conversion mechanism 201 that converts rotation of the motor 200 into linear motion, a rotational angle sensor 202 that detects a rotational angle of the motor 200, and a drive circuit 203 that drives the motor 200. In the valve working angle variable system, as a control shaft 3 is driven by the actuator 2 in an axial direction, the valve working angle variable mechanism 1 operates to thereby vary the valve working angle of an engine valve. The drive circuit 203 of the actuator 2 stores a reference table for an operation quantity of the actuator 2 (stroke of the control shaft 3) and the valve working angle as data.
The actuator 2 is controlled by a command unit 4 that performs various kinds of engine controls including valve working angle control. The command unit 4 calculates an optimum valve working angle according to engine operation status, and gives the drive circuit 203 of the actuator 2 a command.
When a command regarding a valve working angle (a working angle command value) is received from the command unit 4, the drive circuit 203 calculates an operation quantity for the actuator 2 from which the working angle command value can be obtained, as a target operation quantity by looking up the reference table. The drive circuit 203 sets the valve working angle according to the command by rotating the motor 200 so that the current operation quantity of the actuator 2 obtained based on the rotational angle of the motor 200 detected by the rotational angle sensor 202 coincides with the target operation quantity.
FIG. 13 illustrates a configuration for a valve train of an internal combustion engine to which the above valve working angle variable system is applied. As illustrated in FIG. 13, the valve working angle variable mechanism 1 is installed between a cam 6 disposed on a cam shaft 5 and an engine valve 10. The valve working angle variable mechanism 1 is oscillatably supported by a rocker shaft 7 arranged in parallel to the cam shaft 5, and includes an input arm 100 and a pair of output arms 101 arranged on both sides of the input arm 100. Inside the pipe-like rocker shaft 7, the control shaft 3 is slidably arranged in an axial direction.
A roller 102 that abuts on the cam 6 is rotatably mounted on a leading end of the input arm 100 of the valve working angle variable mechanism 1. The input arm 100 is pressed down by the cam 6, and at this time, the input arm 100 oscillates about an axis of the rocker shaft 7 together with the output arms 101.
A projection 103 is formed on an outer circumference of the input arm 100. A lost motion spring 104 is arranged in a compressed state between the projection 103 and a spring seat 8 formed in a cylinder head of the internal combustion engine. The valve working angle variable mechanism 1 is urged so that the roller 102 of the input arm 100 can be pressed against the cam 6 by the lost motion spring 104.
Further, roller rocker arms 9 are arranged below both output arms 101 of the valve working angle variable mechanism 1, respectively. Each of the roller rocker arms 9 is oscillatably supported by the cylinder head of the internal combustion engine through its base end, and abuts on an upper end of the engine valve 10 through its leading end. A roller 11 is rotatably mounted to each roller rocker arm 9. The roller 11 is pressed against a cam surface 105 of the leading end of the output arm 101, which is formed on the side facing the roller rocker arm 9, due to spring force of a valve spring 12 of the engine valve 10.
In this valve train, when the valve working angle variable mechanism 1 oscillates from the cam 6 being pressed down due to the rotation of the cam shaft 5, the cam surface 105 of the output arm 101 presses the roller 11, so that the roller rocker arm 9 oscillates. As the roller rocker arm 9 oscillates, the leading end of the roller rocker arm 9 presses the upper end of the engine valve 10, and as a result the engine valve 10 is driven to open or close. At this time, a contact point between the cam surface 105 of the output arm 101 and the roller 11 of the roller rocker arm 9 reciprocates along the cam surface 105 with the oscillation of the output arm 101. As the distance from the contact point between the cam surface 105 and the roller 11 to the rocker shaft 7 increases, the pressing-down amount of the roller rocker arm 9 by the cam surface 105 and hence the lift amount of the engine valve 10 increases.
In addition, in this valve train, by displacing the control shaft 3 inside the rocker shaft 7 in the axial direction, the relative positions of the leading end of the input arm 100 and the leading end of the output arm 101 in the oscillation direction of the valve working angle variable mechanism 1 can be changed. Due to the change in the relative positions of the leading ends of the input arm 100 and the output arm 101, a reciprocating range of the contact point between the cam surface 105 and the roller 11 changes with the oscillation of the valve working angle variable mechanism 1, and hence, the maximum lift amount and the valve working angle of the engine valve 10 can vary.
Specifically, as the distance between the leading end of the input arm 100 and the leading end of the output arm 101 in the oscillation direction of the valve working angle variable mechanism 1 decreases, the above reciprocating range of the contact point between the cam surface 105 and the roller 11 is displaced so as to be closer to the rocker shaft 7, and thus the maximum lift amount and the valve working angle of the engine valve 10 decrease. Further, as the distance between the leading end of the input arm 100 and the leading end of the output arm 101 in the oscillation direction of the valve working angle variable mechanism 1 increases, the above reciprocating range of the contact point is displaced in a direction in which it moves away from the rocker shaft 7, and so the maximum lift amount and the valve working angle of the engine valve 10 increase.
Next, the internal structure of the valve working angle variable mechanism 1 will be described with reference to FIGS. 14 and 15. As illustrated in FIG. 14, a slider 106 of a substantially cylindrical shape is arranged inside the input arm 100 and the output arms 101 of the valve working angle variable mechanism 1. The slider 106 is integrated with the control shaft 3 and is configured to be rotatable in the axial direction of the control shaft 3. On the outer circumference of the slider 106, an input gear 107 having a helical spline is fixed to a central portion thereof in a longitudinal direction of the slider 106, and output gears 108 having a helical spline are fixed to both sides thereof in the longitudinal direction, respectively.
As illustrated in FIG. 15, an internal toothed gear 109 of an annular shape having a helical spline is formed on the inner circumference of the input arm 100, and an internal toothed gear 110 of an annular shape having a helical spline is formed on the inner circumference of each of the output arms 101. The internal toothed gear 109 of the input arm 100 meshes with the input gear 107 of the slider 106 (FIG. 14), and the internal toothed gear 110 of each output arm 101 meshes with the output gear 108 of the slider 106 (FIG. 14). The helical splines of the input gear 107 and the internal toothed gear 109 differ in an inclined angle from the helical splines of the output gear 108 and the internal toothed gear 110, and are opposite in an inclined direction to the helical splines of the output gear 108 and the internal toothed gear 110.
In this valve train, when the slider 106 is displaced in a co-axial direction with the movement of the control shaft 3 in the axial direction, the input gear 107 meshes with the internal toothed gear 109 and the output gear 108 meshes with the internal toothed gear 110, and so the relative positions of the leading end of the input arm 100 and the leading ends of both output arms 101 in the oscillation direction of the valve working angle variable mechanism 1 change. Specifically, as the slider 106 is displaced in a direction of an arrow L of FIG. 14, the relative positions of the leading end of the input arm 100 and the leading ends of both output arms 101 in the oscillation direction change such that the distance between the leading end of the input arm 100 and the leading ends of both output arms 101 decreases. On the other hand, as the slider 106 is displaced in a direction of an arrow H of FIG. 14, the relative positions change such that the distance between the leading end of the input arm 100 and the leading ends of both output arms 101 increases. Through the change in the relative position, the maximum lift amount and the valve working angle of the engine valve 10 according to the oscillation of the valve working angle variable mechanism 1 with the rotation of the cam 6 can be varied.
The above described valve working angle variable system is an example, and various types of the valve working angle variable systems have been suggested. For example, systems that vary a valve working angle by rotating a control shaft through an actuator and so driving a valve working angle variable mechanism have been suggested.
Conventionally, an internal combustion engine including a valve working angle variable system is disclosed in Patent Document 1. The internal combustion engine disclosed in Patent Document 1 includes a valve timing variable system that varies valve timing in addition to a valve working angle variable system. In the internal combustion engine including the two variable systems, when a valve working angle increases in a state in which valve timing is controlled near a piston top dead point, interference between the engine valve and the piston, so-called valve stamping may occur. Thus, in the system disclosed in Patent Document 1, by limiting a control range of a valve working angle according to current valve timing or by limiting a control range of valve timing according to a current valve working angle, the occurrence of valve stamping is avoided.